With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 10 has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, and intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.
The gas turbine engine 10 works in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.
The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.
Conventionally, a compressor rotor stage comprises a plurality of radially extending blades mounted on a disc. The blades are mounted on the disc by inserting a root portion of the blade in a complementary retention groove in the outer face of the disc periphery. To ensure a radially smooth inner surface for air to flow over as it passes through the stage, annulus fillers can be used to bridge the spaces between adjacent blades. Typically, a seal between the annulus fillers and the adjacent fan blades is also provided by resilient strips bonded to the annulus fillers adjacent the fan blades.
Annulus fillers of this type are commonly used in the fan stage. The fillers may be manufactured from relatively lightweight materials and, in the event of damage, may be replaced independently of the blades
It is known to provide annulus fillers with features for removably attaching them to the rotor disc. An annulus filler may be provided with a hook member at its axially rear end, the hook member sliding into engagement with part of the rotor disc and/or a component located axially behind the rotor assembly, for example a rear fan air seal. Typically, such an annulus filler is slid axially backwards over the rotor disc following an arc which matches the chord-wise curvatures of the aerofoil surfaces of the adjacent blades until the hook member engages, and is then retained in place by a front attachment disc which is fastened over the fronts of all the annulus fillers located around the rotor disc.
US 2010/0040472 proposes another form of annulus filler having an outer part which defines an airflow surface for air being drawn through the engine and a separate support part which is connectable to the outer part and to the rotor disc to support the outer part on the rotor disc. The support part spaces the outer part from the rotor disc and has an inter-engaging portion that in use connects to the rotor disc and has a further inter-engaging portion that in use connects to the outer part. The support part can be fitted first to the disc and the outer part fitted to the support part thereafter.
U.S. Pat. No. 4,655,687 proposes an annulus filler that can be fitted to the rotor disc in a radial direction of the disc. The annulus filler that has a salient foot that is shaped similarly to re-entrant grooves formed in the disc rim between pairs of adjacent blades. The foot is proportioned so as to pass radially of the disc through the neck of a respective groove. Wedges positioned between opposing walls of the grooves and respective feet then prevent withdrawal of the feet in a direction radially outwardly of the disc.